Though according to some conventional methods for sterilizing long tubules, such as catheters and endoscopes, ultraviolet rays or high pressure steam is used, the efficiency of sterilization is low, and in some cases the material changes in quality due to the ultraviolet rays or heat. Though other conventional methods using ethylene oxide gas, liquid hydrogen peroxide and steam are highly effective, ethylene oxide and hydrogen peroxide are poisonous, and hydrogen peroxide can be harmful to the handler if it gets on the clothes. In addition, liquids and gases do not reach deep inside the long tubule, due to their viscosity, in accordance with methods other than those using ethylene oxide, and ultraviolet rays are insufficiently transmissive to do so, and thus, it is difficult to sufficiently sterilize long tubules.
Sterilizing methods using plasma have also been proposed, and according to that in Patent Document 1, an electric discharge wire is inserted into the long tubule, so that discharge plasma is generated between the center electrode formed in the discharge wire and an external electrode. According to this method, the discharge wire and an electricity supply wire for supplying power to the discharge wire need to be inserted into the long tubule.    Patent Document 1: Japanese Unexamined Patent Publication 2003-210556
However, it is difficult to make the outer and inner diameter of the discharge wire small in order to avoid conduction between the center electrode and the external electrode and secure a space for discharge between the two, and it is also necessary for the wire to be thick enough, and for insulation between the wires to be secured in order to prevent insulation breakdown in the electricity supply wire. Thus, the long tubules to be sterilized are limited to those having a large inner diameter (for example of 5 mm or more, or 1 cm or more), and in addition, the inner wall of long tubules easily scratches when the discharge wire and electricity supply wire are inserted and removed. Furthermore, when the discharge wire or electricity supply wire makes contact with the inner wall after the sterilization process, bacteria and the like on the surface stick to the inner wall, causing secondary infection. In the case where the same device is used for sterilization, secondary infection becomes a significant problem.
The following Non-Patent Document 1 discloses a sterilizing system for catheters under atmospheric pressure. In this sterilizing system, a wire electrode is inserted into the tubule so that a plasma flow is generated between the wire electrode and a grounding electrode outside the tubule.    Non-Patent Document 1: TOPICS “Development of sterilizing systems using non-equilibrium plasma flow under atmospheric pressure,” Journal of Japan Society of Mechanical Engineers, Vol. 110, No. 1063, pp. 56, June 2007.
As in the case of the above described Patent Document 1, however, the insertion of a wire electrode into the tubule risks damaging the inside or causing secondary infection. In addition, there is a risk that the wire electrode may sputter because of the plasma, or that the metal that forms the electrode may make contact with the inside of the tubule along the entire length and causing contamination.
Furthermore, the region where plasma is generated inside the tubule is highly localized between the wire electrode and the grounding electrode. Therefore, a moving mechanism or the like is required in order to move the tubule and the electrodes relative to each other and sterilize the entirety of the inside, making the structure complex and increasing the risk of the inside or outside of the tubule getting damaged, as well as secondary infection. In the case where the grounding electrode is in cylindrical form so that it can surround the tubule, it is necessary to prepare grounding electrodes of different diameters for tubules of different diameters. In addition, there is a risk that the outside of the tubule may be damaged or infected, because the tubule and the grounding electrode are close to each other. Even in the case where the diameter of the grounding electrode is large enough to accommodate for tubules of different diameters, the distance between the wire electrode and the grounding electrode is great, and thus the voltage to be applied to the electrode is high, and as a result, there is a high risk that the wire electrode or the grounding electrode may sputter because of the plasma and contaminate the tubule.